Brannon repeatedly attacked Tillis's conservative credentials throughout the night, arguing he wasn't right enough on a raft of issues.

Tillis largely focused his ire for Sen. Kay Hagan (D-N.C.), who he's hoping to face this fall. But on a handful of occasions he battled with Brannon — including on one where he disagreed with Brannon about laws keeping guns out of the hands of the mentally ill.

"Violent felons and people with mental health problems need to be rehabilitated, and they need help," he said after Brannon expressed skepticism about any national gun control laws and questioned whether states should limit access to guns for most mentally ill citizens. "You can't put a gun in the hand of someone who represents a danger to themself or to society. I understand the concept Dr. Brannon said in his words about the Second Amendment, but folks, this is about being practical."

Brannon, Tillis, Rev. Mark Harris and nurse Heather Grant (R) all said they don't believe man-caused climate change is an established scientific fact.

Tillis also gave Democrats some possible ammunition for the general election, saying he'd consider shutting down the Department of Education and doubling down on his view that there shouldn't be a federal minimum wage and that it should be determined by the states.

The debate is the first of three over the next week. Tillis is hoping to win the May 6 primary outright by topping 40 percent and avoid a runoff against Brannon or Harris, who largely stayed out of the fray on Wednesday.